This invention relates to a transformer for use in high frequency switching power supplies, for supplying regulated low voltage high current power at high energy efficiency, which is especially suitable for, but not limited to, use in power supplies for high performance computers.
Supercomputers and other high performance computers typically require several kilowatts to several hundred or more kilowatts of power to be supplied at one or more low voltages in the range of 1.5 to 6.0 volts D.C.
Each required voltage requires a separate power supply. As power requirements increase, power supply units are operated in parallel, sharing the required load current for each voltage bus.
It is desirable to have these computers occupy as small a volume as possible, and that their power supplies also occupy a small volume (high power density) and have high energy efficiency to minimize heat loss in these power supply units.
Power supplies presently available are capable of meeting these requirements to only a limited extent; a primary limitation being the leakage inductance of the converter transformer. While the high frequency primary voltage may have a duty cycle (on time to total cycle time ratio) of 0.95, the duty cycle for energy transfer from the primary to the secondary winding of the converter transformer is limited by (i) the leakage inductances, (ii) the primary current, which is the load current reduced by the primary to secondary turns ratio, and (iii) the switching frequency. All other things being equal, an increase in switching frequency will further reduce the energy transfer duty cycle.
For a given output power, anything that reduces the energy transfer duty cycle requires a compensating reduction of the primary to secondary turns ratio. This reduction in turns ratio increases the RMS current in the primary circuits, increasing losses and reducing throughput efficiency.
Typical power supplies currently available use two to four or more converter transformers to achieve higher output power in a "single" power supply unit..sup.1 This approach generally requires a higher component count in the power portion of the units, which is likely to reduce reliability. FNT .sup.1 Multiple converter transformer topologies typically are employed for units having an output of two kilowatts or more.
Accordingly, an object of the present invention is to provide an improved high energy efficiency transformer on a single permeable core structure having a low voltage high current secondary winding that will permit the implementation of higher power density, highly efficient power supply units.